1. R.V.Ambartsumian, V.S.Letokhov, E.A.Ryabov, N.V.Chekalin: ZhETF Pis. Red.20, 597 (1974)
2. R.V.Ambartzumian, Yu.A.Gorokhov, V.S.Letokhov, G.N.Makarov, E.A.Ryabov, N.V.Chekalin: Kvantovaja Elektronica2, 2197 (1975)
3. V.S.Letokhov, C.B.Moore. Kvantovaja Electronica:3, 248, 485 (1976)
4. V.S.Letokhov, C.B.Moore:Chemical and Biochemical Applications of Lasers, ed. by C.B.Moore, Vol. 2 (in press)
5. R.V.Ambartsumian, Yu.A.Gorokhov, V.S.Letokhov, G.N.Makarov, A.A.Puretsky: Phys. Lett.56A, 183 (1976); also ZhETF Pis. Red.22, 7, 374 (1975)